function Bullet(options) {
    this.init(options);
}

Bullet.prototype = new Sprite();

Bullet.prototype.radius = 5;
Bullet.prototype.speed = 40;

Bullet.prototype.move = function() {
    var borders = this.borders();
    this.baseMove();
    if(borders.maxX < 0 || borders.minX > canvas.width
       || borders.maxY < 0 || borders.minY > canvas.height) {
        disappear(bullets, this);
    }
};

Bullet.prototype.draw = function() {
    ctx.beginPath();
    ctx.arc(this.centerX, this.centerY, this.radius, 0, 2 * Math.PI);
    ctx.stroke();
};

